(1) The present invention relates to a tubular multilayer woven fabric, i.e., a three-dimensional multilayer woven fabric having a tubular cross section and formed by arranging a non-interlaced circumferential yarn on an intermediate position thereof, and a method for manufacturing the tubular multilayer woven fabric.
(2) Description of the Related Art
Various three-dimensional woven fabrics have been disclosed; for example, Japanese Examined Patent Publication (Kokoku) No. 52-39473 discloses a three-dimensional multilayer woven fabric formed by arranging a plurality of warp yarns and a plurality of weft yarns in a horizontal direction and a vertical direction and binding the warp yarns and the weft yarns to each other by a plurality of binding yarns to form one body. Further a tubular three-dimensional woven fabric having one layer formed by arranging a plurality of yarns along an axial direction of a mandrel, on a circumferential surface of the mandrel, and interlacing or weaving a yarn in a direction perpendicular to the axial yarns into the axial yarns, is known.
The three-dimensional multilayer woven fabric obtained by the method disclosed in Japanese Examined Patent Publication (Kokoku) No. 52-39473 is only a woven fabric having a rectangular cross section, and although a tubular three-dimensional woven fabric can be obtained by the latter method, the obtained woven fabric has one layer and thus a tubular woven fabric having a thick thickness cannot be obtained by this method.
A fiber reinforced tubular molded piece obtained by using a woven fabric of a glass fiber, a carbon fiber or the like as a reinforcing material of a resin or the like is known, and the following typical manufacturing methods for the fiber reinforced tubular molded piece, e.g., a fiber reinforced pipe, are known but have the following disadvantages:
1. A method of weaving a flat woven fabric of the glass fiber, the carbon fiber or the like, and then rolling the obtained woven fabric to form a circular shape when making a reinforcing body.
Since the reinforcing body having the circular shape manufactured by this method has a join line along an axial direction of the reinforcing body, a problem arises in that a strength against a stress applied in a circumferential direction of the tube becomes irregular and thus the molding ability of this method is low;
2. A method of weaving a tape-like woven fabric of the glass fiber, the carbon fiber or the like, and winding the tape-like woven fabric in a spiral state on a support to make a reinforcing body.
A molding ability in a process of this method is relatively simple compared with that of the above method 1, but a spirally joining line extends in an axial direction in a molded piece obtained by this method and thus a problem arises in that a strength against a stress applied in an axial direction of the tube is not sufficiently high; and
3. A method of weaving a tubular woven fabric of a glass fiber, a carbon fiber, or the like to make a one layer tubular woven fabric, and piling at least two layer tubular woven fabrics on each other to make a reinforcing body.
When this reinforcing body is made, if the tubular woven fabric having the same number of yarns per unit length in an axial yarn and an circumferential yarn are manufactured, a pipe having the same strength in the axial direction and the circumferential direction can be obtained.
It is well known that, when a pressure is applied to a pipe from an inside or an outside, a stress generated in a circumferential direction becomes twice as much as a stress generated in an axial direction. Accordingly, if a relatively large strength is not required for the circumferential strength, it is possible to make the number of yarns per unit length in the axial direction approximately half the number of yarns per unit length in the circumferential direction. When it is necessary to improve the circumferential strength, however a problem arises in that, since the circumferential yarn must be interlaced with the axial yarns, there is a maximum limit to the number of yarns per unit length of the circumferential yarn. Further, the circumferential yarn in the tubular woven fabric has a wave-like shape due to being woven with the axial yarn, and strain in the circumferential direction is generated in a tube by a curve-like deformation of the circumferential yarn, and thus it is impossible to attain a high reinforcing effect. For the above reason, when it is intended to increase the strength in the circumferential direction of the tubular woven fabric, usually an additional reinforcing filament is wound on a surface of the tubular woven fabric, but this procedure is cumbersome and thus a problem arise in that the productivity of this type tubular woven fabric is lowered.